Add lower bounds of package versions to cabal file

I added lower bounds of package versions to ```.cabal``` file. This should compile on GHC 7.4.2 and the latest Haskell Platform, but I can't verify that since I use 7.6.1. I noticed that you didn't have ```hoogle``` as a dependency - I suppose this is an accidental omission. Also, ```mueval``` is gone from the dependencies and I don't know whether this is intended or not. Just in case I left this dependency commented out.

I made my changes on a separate branch so that you don't have to merge them immediately into the master if there are any corrections to make (e.g. the ```mueval``` dependency should be uncommented or removed).